This application is based upon and claims the benefit of priority of Japanese Patent Application No. 2000-284633 filed on Sep. 20, 2000, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an electromagnetic actuator having a coil bobbin, a magnetic coil, a yoke, a fixed core and a moving core, which is a solenoid valve applicable, in particular, to a hydraulic control apparatus of an automatic transmission for vehicles.
2. Description of Related Art
Conventionally, in an electromagnetic actuator for driving a spool accommodated to move axially in a housing that is provided in a hydraulic system circuit of an automatic transmission for a vehicle, as shown in FIG. 9, a solenoid portion 100 is composed of a stator core 101, a coil bobbin 102 fixed to a radial outer circumference of the stator core 101, a magnetic coil (solenoid coil) 103 wound on the coil bobbin 102, a moving core housed inside the stator core 101 and a yoke 105 positioned on an outer circumferential side of the magnetic coil 103. The moving core 104 is attracted axially in the stator core 101 by magnetic force exerted on energizing the magnetic coil 103.
The coil bobbin 102 and the magnetic coil 103 constitute a coil assembly 106. The stator core 101, which is arranged on inner circumferential side of the coil assembly 106, has first and second flanges 111 and 112 between which the coil assembly 106 is axially sandwiched. The coil bobbin 102 has first and second flange portions 121 and 122 between which the magnetic coil 103 is wound. The yoke 105 is shaped as a cylinder having a bottom wall 151 at an axial end thereof.
According to the conventional solenoid portion 100, the stator core 101 is manufactured by plastic working (cold forging) in use of separable molding dies whose constructions are complicated since the stator core 101 is provided at axial opposite ends thereof with the first and second flanges 111 and 112. Accordingly, the conventional stator core 101, whose manufacturing is not easy from a standpoint of its construction, has a drawback that the manufacturing cost is higher. Further, in the conventional solenoid portion 100, each dimensional accuracy of an inner diameter of the yoke 105 and an outer diameter of the stator core 101 over a whole axial length thereof is required when the stator 101 is assembled to the yoke 105 because it is important for securing better product performance to minimize a magnetic gap between the outer circumference of the stator core 101 and the inner circumference of the yoke 105, resulting in lower working efficiency and less manufacturing productivity.
In view of the above-described problem, it is an object of the present invention to provide an electromagnetic actuator having first and second magnetic elements to be manufactured without using dividable complicated molding dies so that the manufacturing cost of the electromagnetic actuator is lower.
It is an aspect of the present invention to provide the electromagnetic actuator in which a magnetic gap between the first and second magnetic element is minimized so that product performance of the actuator is improved.
To accomplish the above-described object, the electromagnetic actuator has a magnetic coil for generating magnetic force when energized, a cylindrical resin molding member having first and second flange portions between which the magnetic coil is wound, a moving core positioned at a radial inside of the resin molding member and axially movable due to the magnetic force generated on energizing the magnetic coil and first and second magnetic element to be magnetized by the magnetic force generated on energizing the magnetic coil.
With the electromagnetic actuator, the first magnetic element is positioned at a radial outside of the magnetic coil and provided at an inner circumference of an axial end thereof with a first protruding portion extending radially inward. The second magnetic element is disposed between a radial outside of the moving core and a radial inside of the magnetic coil and provided at an outer circumference of an axial end thereof on a side opposite to the axial end of the first magnetic element with a second protruding portion extending radially outward. The first and second flange portions are axially sandwiched between and supported by the first and second protruding portions.
It is preferable that the first magnetic element is provided at the other axial end thereof with an opening whose inner circumference is fitted to an outer circumference of the second protruding portion and the first protruding portion is provided in a center thereof with an inner recess whose inner circumference is fitted to an outer circumference of the second magnetic element. Accordingly, to minimize the magnetic gap, only limited surfaces of the first and second magnetic elements, which are fitted to each other for assembly, need accurate dimensions.
Another object of the invention is to provide a method of manufacturing an electromagnetic actuator whose parts and components are assembled from the same side, resulting in improving assemble efficiency and manufacturing productivity.
To achieve the object, in an electromagnetic actuator having a magnetic coil, a yoke, a moving core and a fixed core, while the yoke made of magnetic material is formed in shape of a cylinder having a bottom at an axial end and an opening at the other axial end, the moving and fixed cores both made of magnetic material are formed in a given shape, respectively. Then, the moving core is assembled to the yoke by axially moving and inserting the moving core into an inside of the yoke from the opening of the yoke toward the bottom thereof. On the other hand, after forming a primary resin part having first and second flange portions on an outer circumference of the fixed core by integral resin molding and, then, winding the magnetic coil on the primary resin part between the first and second flange portions, a secondary resin part is formed over an outer circumference of the magnetic coil by integral resin molding. Accordingly, a coil assembly, in which the magnetic coil and the primary and secondary resin parts are integrated with the fixed core, is completed. Then, the coil assembly is assembled to the yoke by axially moving and inserting the coil assembly into a space between an inner circumference of the yoke and an outer circumference of the moving core from the opening of the yoke toward the bottom thereof.